1. Field of the Invention
This invention relates to an apparatus for starting the drive of a load by a high-voltage battery. This invention particularly relates to an apparatus designed so that the voltage of a high-voltage battery is applied to a load when a switching element is moved to its on state.
2. Description of the Related Art
A typical mobile robot includes a motor for moving a robot body, and a motor for driving a robot arm. When the robot is connected with an external power supply, the motors are activated by the external power supply. The robot has an internal power supply using a lead-acid battery. During movement of the robot body, the robot remains disconnected from the external power supply, and the motors are activated by the internal power supply.
Generally, the motors in the robot are of the AC (alternating current) type. The robot includes an inverter which can receive DC (direct current) power from the internal power supply. The inverter converts the DC power into AC power fed to the motors. In general, the rating drive voltage for the motors is 200 V while the voltage of the internal power supply is 24 V. In this case, the voltage of the internal power supply is boosted to 280 V, and the 280-V DC power is fed to the inverter.
The degree of the voltage boost (24 V to 280 V) is relatively high. Therefore, the voltage boost causes a considerable energy loss. As a result, the internal power supply is required to be frequently charged, and the availability factor of the robot tends to be low.
It is conceivable to replace the 24-V internal power supply with a 280-V internal power supply. In this case, the voltage of the internal power supply is directly applied to the inverter. Thus, it is unnecessary to boost the voltage of the internal power supply. The 280-V internal power supply consists of a combination battery or a high-voltage battery having cells coupled together in series.
The inverter is selectively connected with and disconnected from the internal power supply by a switching element using a semiconductor switching device. The voltage across the 280-V internal power supply is too high to drive the semiconductor switching device. Thus, it is necessary to provide an auxiliary low-voltage battery for driving the semiconductor switching device. The auxiliary low-voltage battery increases the weight of the robot.
It is an object of this invention to provide an apparatus for starting the drive of a load by a high-voltage battery which dispenses with an auxiliary low-voltage battery for driving a switching device.
A first aspect of this invention provides an apparatus for starting the drive of a load by a high-voltage battery. The apparatus comprises a combination battery including a plurality of cells connected together in series; a power feed path between the combination battery and the load; a switching element for selectively blocking and unblocking the power feed path, the switching element being changed to its on state when receiving a drive voltage; a starting switch; a drive circuit connected with at least one cell among the cells in the combination battery and using said at least one cell as a power source to generate the drive voltage when the starting switch is moved to its on position, the drive circuit applying the drive voltage to the switching element; a power supply circuit connected with the power feed path and the switching element, and receiving an output voltage from the combination battery and starting to operate when the switching element is changed to its on state, the power supply circuit dropping the output voltage from the combination battery to generate a dropped voltage; and means for changing a power source for setting the switching element in its on state from said at least one cell to the power supply circuit in response to the dropped voltage generated by the power supply circuit.
A second aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the changing means comprises a relay including a drive coil and a relay switch, and the relay switch changes the power source for setting the switching element in its on state from said at least one cell to the power supply circuit when the dropped voltage generated by the power supply circuit is applied to the drive coil.
A third aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the changing means comprises 1) means for setting the dropped voltage generated by the power supply circuit to a level higher than an output voltage of said at least one cell, and 2) means for connecting the drive circuit to both said at least one cell and the power supply circuit, wherein the output voltage of said at least one cell is applied to the drive circuit and the switching element is changed to its on state when the starting switch is moved to its on position, and wherein after the power supply circuit is started to operate, the dropped voltage generated by the power supply circuit is applied to the drive circuit and the switching element is kept in its on state.
A fourth aspect of this invention is based on the third aspect thereof, and provides an apparatus further comprising a rectifying element provided in a power feed line connected between the drive circuit and said at least one cell, the rectifying element allowing a flow of a current from said at least one cell to the drive circuit and blocking a flow of a current from the drive circuit to said at least one cell.
A fifth aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising means provided in a power feed line between the changing means and said at least one cell for sensing a current flowing in the power feed line, and detecting a changing state of the changing means in response to the sensed current.
A sixth aspect of this invention is based on the first aspect thereof, and provides an apparatus further comprising a rectifying circuit for converting an AC power into a DC power, and means for feeding the DC power to the load.
A seventh aspect of this invention provides an apparatus for starting the drive of a load by a high-voltage battery. The apparatus comprises a combination battery including a plurality of cells connected together in series, the combination battery having a tap between its hot end and its cold end; a power feed path between the combination battery and the load; a switching element being changed to an on state when receiving a drive voltage, and being changed to an off state when being released from the drive voltage, the switching element unblocking the power feed path when being changed to the on state, and blocking the power feed patch when being changed to the off state; a starting switch movable to an on position; first means for, when the starting switch moves to the on position, generating a first control voltage from a voltage at the tap of the combination battery and applying the first control voltage to the switching element as the drive voltage to change the switching element to the on state; second means for generating a second control voltage from an output voltage of the combination battery when the switching element is changed to the on state by the first means; and third means for applying the second control voltage to the switching element as the drive voltage instead of the first control voltage to keep the switching element in the on state.